Method for producing color filter comprising an inorganic active layer and photoresist

ABSTRACT

The method for producing a color filter of the present invention comprises the following steps: an inorganic active layer is formed on a transparent substrate, a first color is dyed on said inorganic active layer, a resist is formed on portions of the inorganic active layer other than portions where a second color is dyed, a decoloring treatment is conducted, the second color is dyed on the exposed inorganic active layer, the resist is removed, a resist is formed on portions of the inorganic active layer other than portions where a third color is dyed, a decoloring treatment is conducted, the third color is dyed on the exposed inorganic active layer, and then the resist is removed.

FIELD OF THE INVENTION

The present invention relates to a method for efficiently producing acolor filter superior in various kinds of physical properties.

BACKGROUND ART

The following color filters have been used for various kinds of displayssuch as a liquid crystal display.

1. A color filter obtained by forming a polymer film superior indyeability on a transparent substrate and then patterning the polymerfilm by photolithography followed by coloring.

2. A color filter obtained by forming a polymer film superior indyeability on a transparent substrate and then drawing a color filterpattern with dye.

3. A color filter obtained by forming a pigmented polymer film patternon a transparent substrate by photolithography.

4. A color filter obtained by forming a transparent electroconductivefilm pattern, e.g. an ITO film pattern, on a transparent substrate andthen applying an electrodepositable paint on the transparentelectroconductive film.

5. A color filter obtained by forming a colored polymer film on atransparent substrate by a printing method.

However, the above described color filters have the followingdisadvantages.

The color filter of the method 1 is poor in surface flatness andstrength.

The color filter of the method 2 is superior in surface flatness,because the polymer film is not patterned but colored as a colorpattern. The filter, however, is poor in surface strength, because itemploys polymer material. Also, since the patterns of the respectivecolors are colored on the same one polymer film, bleeding and migrationof the dyes occurs.

Since the color filter of the method 3 is obtained by coloring thepolymer film on the transparent substrate in the same manner as thecolor filter 1, it is poor in surface flatness and surface strength. Inaddition, a problem may occur in that light is scattered by pigmentparticles.

In the production of the color filter of the method 4, the patternedtransparent electroconductive film has to be formed, and it is furtherrequired in many cases that a transparent electrode from ITO and thelike is formed on the electrodeposited coat, so that the producingprocess becomes complicated. In addition, since the electrodepositablepaint is applied on the transparent film pattern, the obtained colorfilter is poor in surface flatness.

The color filter of the method 5 is also poor in surface strength,because it employs polymer material as mentioned in the method 1.

It is an object of the present invention to solve the above describedproblems and provide a method for efficiently producing a color filtersuperior in various kinds of physical properties.

DISCLOSURE OF INVENTION

In order to achieve the above described object, the method for producinga color filter of the present invention comprises the following steps:an inorganic active layer is formed on a transparent substrate, a firstcolor is dyed on said inorganic active layer, a resist is formed onportions of the inorganic active layer other than portions where asecond color is dyed, a decoloring treatment is conducted, the secondcolor is dyed on the exposed inorganic active layer, the resist isremoved, a resist is formed on portions of the inorganic active layerother than portions where a third color is dyed, a decoloring treatmentis conducted, the third color is dyed on the exposed inorganic activelayer, and then the resist is removed.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1(a-j) and 2(a-m) are sectional views showing the manufacturingprocess of the color filter according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is described in more detail with reference to thedrawings.

In FIGS. 1(a-j) and 2(a-m), the numeral 1 designates a transparentsubstrate, the numeral 2 designates an inorganic active layer and thenumeral 3 designates a resist.

At first, the inorganic active layer 2 is formed on a surface of thetransparent substrate 1 [see FIG. 1 (a)].

The transparent substrate 1 may be formed from materials used forvarious kinds of displays (e.g. a liquid crystal display), for example aglass plate, a synthetic resin plate or a synthetic resin film. It ispreferable that the glass plate is formed of transparent glass, such assoda-lime glass, aluminosilicate glass, boron silicate glass, bariumborosilicate glass and the like.

On the transparent substrate 1, an inorganic active layer 2 preparedfrom porous inorganic substances is formed. The following sol-gel methodis suitable for a method of forming the inorganic active layer 2. Thus,a sol is obtained by hydrolyzing in an aqueous medium a compoundexpressed by the following formula;

    M(OR.sub.1).sub.m (OR.sub.2).sub.n X.sub.p Y.sub.q         (I)

wherein M is at least one element selected form the group consisting ofmagnesium, calcium, zirconium, titanium, hafnium, germanium, yttrium,aluminum, gallium, tin and silicon; R₁ and R₂, which are the same ordifferent, show a hydrogen atom, an alkyl group or an acyl group,respectively; X and Y, which are the same or different, show a hydrogenatom, a chlorine atom or a hydroxyl group, respectively; m, n, p and qare an integer of 0 to 8, respectively, so as to meet m+n+p+q=a valenceof M;

and then degelatinizing. The obtained sol is applied onto thetransparent substrate 1 and baked. The compounds expressed by thegeneral formula (I) include tetraethyl silicate, aluminumtri-isopropoxide, titanium tetrabutoxide, zirconium tetrabutoxide, apartially hydrolyzed product thereof and the like. The aqueous mediumcontains a necessary quantity of water, catalyst for the hydrolysis(such as hydorochloric acid, sulfuric acid, nitric acid and acetic acid)and alcohol. The method of applying the sol to the surface of thetransparent substrate 1 includes a bar coating method, a roll coatingmethod, a spin coating method, a dipping method and the like. The abovedescribed sol is applied onto the surface of the transparent substrate 1and then dried followed by baking at temperatures of 300° to 600° C.,whereby obtaining an inorganic active layer 2. It is preferable that athickness of the inorganic active layer 2 is about 1 to 20 μm.

Next, the inorganic active layer 2 is dyed in a first color with a dye[see FIG. 1(b)]. It is preferable that acid dye, acid mordant dye, dyefor aluminum, direct dye, oil-soluble dyes and the like are used as thedye. The color to be dyed may be red (R), green (G) or blue (B) for acolor filter. Here, red (R) is selected for convenience.

Subsequently, a resist 3a is formed on portions other than portionswhich are colored with a second color [see FIG. 1(c)]. If the secondcolor is green, the portions to be covered with the resist 3a would beportions which are not colored with green (G). The resist is formed inthe desired pattern of the color filter. In addition, it is preferablethat a suitable resist, such as photoresist and printing resist, is useddepending upon the accuracy of the pattern, cost and the like.

Next, the dye on portions which are not covered with the resist 3a isdecolored [refer to FIG. 1(d)]. It is preferable that nitric acid,sodium hypochlorite, sulfuric acid or the like are used for thedecoloring treatment. The inorganic active layer 2 on the portions whichare not covered with the resist 3a became transparent again by thedecoloring treatment and merely the portions which have been coveredwith the resist are colored in red (R).

Further, the inorganic active layer 2 is dyed in the second color [referto FIG. 1(e)]. Here, green (G) is selected as the second color. Sincethe portions which have been dyed with red (R) in the previous coloringstep are covered with the resist 3a, portions other than the resistcovered portions are dyed in green (G).

Successively, the resist 3a is removed [see FIG. 1(f)].

Next, a resist 3b is formed on portions other than portions which are tobe dyed in a third color, as described above [see FIG. 1(g)]. If thethird color is blue, the portions to be covered with the resist 3b wouldbe portions which are not colored with blue (B).

Next, the dye on portions which have not been covered with the resist 3bis decolored [see FIG. 1(h)]. The portions which have not been coveredwith the resist 3b but dyed in the first color, i.e. red (R), of theinorganic active layer 2 become transparent again.

Successively, similar processes are repeated to dye the inorganic activelayer 2 by the third color, that is blue (B), [see FIG. 1(i)].

Finally, the resist 3b is removed to obtain the color filter [see FIG.1(j)].

In the case where the color filter of three colors, that is R, G and B,is produced by the above described method, the patterning is required inonly two times of dyeing in green (G) and blue (B), but the patterning,such as formation of resist, masking and etching, is not required in thedyeing in red (R). Moreover, since the dye to be decolored in the abovesteps is the dye of the first color (i.e. red (R)), it is preferred thata dye which is easily decolored is used as the first color to ensure thereliability of decoloring.

In the case where a black mask is required for the color filter, it canbe formed by a chemical plating method or a dyeing method. The processfor forming the black mask may be conducted either before any one of thedyeing steps of the first to third colors or after any one of the dyeingsteps of the first to third colors. In particular, it is preferred thatthe black mask is formed after dyeing the first color followed by dyeingthe second and third colors, because the black mask can be utilized asan alignment mark when dyeing the second and third colors. Forconvenience, in the present specification, the black mask is formed bythe chemical plating method after the dyeing step of the third color.

At first, an inorganic active layer 2 is formed on a transparentsubstrate 1 [see FIG. 2(a)] and colored with a first color [see FIG.2(b)].

Next, a resist 3a is formed on portions other than portions which are tobe colored with a second color [see FIG. 2(c)]. In this time, the resist3a is also formed on portions on which a black mask is to be formed.

Subsequently, after a decoloring treatment is conducted [see FIG. 2(d)],the exposed inorganic active layer 2 is colored with the second color[see FIG. 2(e)], and the resist 3a is then removed [see FIG. 2(f)].

A resist 3b is then formed on portions other than portions which are tobe colored with a third color [see FIG. 2(g)]. In this time, the resist3b is also formed on portions on which the black mask is to be formed.

After conducting a decoloring treatment [see FIG. 2(h)], the exposedinorganic active layer 2 is colored with the third color [see FIG. 2(i)]and the resist 3b is removed [see FIG. 2(j)].

Next, a resist 3c is formed on portions other than portions on which theblack mask is to be formed [see FIG. 2(k)].

A decoloring treatment is conducted to only decolor the portions onwhich the black mask is to be formed, because the portions which havebeen colored with other three colors of R, G and B are covered with theresist 3c.

Next, the transparent substrate 1 is subjected to the chemical platingto form the black mask between the respective colors of R, G and B [seeFIG. 2(l)].

It is preferable that the chemical plating is conducted by the use ofmetals more noble than copper. The metals more noble than copper includegold, silver, palladium, platinum, rhodium and ruthenium. The reason whythe metals more noble than copper are used is that the portions having ametallic gloss are easily removed after plating and the ground portionsexhibit a chemical concentration of 3.0 or more after said portionshaving a metallic gloss are removed.

The chemical plating can be conducted by the use of the conventionalmethods. For example, according to the "Electroless Plating" (written byTokuzo Kanbe), a mixture of the following solution 1 and solution 2 in aratio of 1:1 can be used as a silver plating bath.

    ______________________________________                                        The solution 1:                                                               Silver nitrate         20     g                                               Ammonia water     suitable quantity                                           Water                  1,000  ml                                              The solution 2:                                                               Sodium potassium tartarate                                                                      100 g/300 ml                                                Water             to 700 ml in all                                            ______________________________________                                    

The transparent substrate 1, which has been colored in 3 colors of R, Gand B, is immersed in the above described silver plating bath for 30seconds to 5 minutes and then pulled up from the bath followed byremoving the portions having metallic gloss, whereby the black mask canbe chemically plated merely between the portions dyed in the respectivecolors of the color filter.

The portions having metallic gloss deposited on the surface of theinorganic active layer 2 are wiped off by the use of soft substances,such as cloth, paper and rubber spatula, in order to remove the portionshaving metallic gloss. Merely the portions having metallic gloss areremoved by this operation and the black portions, which have beencontained in the inorganic active layer 2, remain as they are. The blackmask formed in this manner is completely black as seen from either sideof the transparent substrate and does not exhibit metallic gloss at all,which is optimum for the black mask. In addition, the section of theobtained black mask was investigated by an optical microscope with theresult that black color spread itself from the surface of the inorganicactive layer 2 to the deepest portion of the inorganic active layer 2,that is the boundary surface of the inorganic active layer 2 and thetransparent substrate 1.

Finally, the resist 3c is removed to obtain the color filter with theblack mask formed thereon [see FIG. 2(m)].

The black mask may be formed by a nickel plating method using apalladium-tin catalyst in place of the above described silver platingmethod. In the nickel plating method, the following steps are conductedin the recited order.

(1) A step of forming the resist on the portions other than the portionson which the black mask is to be formed.

(In the case where the inorganic active layer has been dyed, a step ofdecoloring)

(2) A step of absorbing a catalyst solution into the inorganic activelayer.

(3) A step of activating the catalyst solution.

(4) A step of plating metal.

(5) A step of removing the resist.

Thus, the metals are plated merely on the portions into which theactivated catalyst solution has been absorbed. The step (5) of removingthe resist in this process may be conducted immediately after the step(2) of absorbing the catalyst solution into the inorganic active layer.In this method, plating can be conducted even without decoloring theinorganic active layer 2 on the portions on which the black mask is tobe formed. In addition, in this method, no practical trouble comes upeven though the portions having metallic gloss are not removed.

Finally, the resist 3c is removed to obtain the color filter with theblack mask formed thereon.

Instead of the chemical plating method, the black mask may be formed bydyeing between the portions which have been dyed in the respectivecolors of R, G and B, in black. Besides, in order to form the black maskby the dyeing method, at first the black mask may be formed andthereafter colored in colors of R, G and B. In short, according to thedyeing method, four colors of R, G, B and black can be dyed in any orderby repeating the process comprising the steps of dyeing, the steps offorming the resist and the step of decoloring.

As described above, in the case where the black mask is formed by thechemical plating method or the dyeing method, the patterning by theresist is conducted merely 3 times, that is, the number of the steps canbe reduced.

In the above described processes, the step of forming the resist and thestep of decoloring are separately conducted. However, in a certainspecified case where the resist is a photoresist capable of beingdeveloped by an alkaline developer and the dye of the first color isdecomposed or extinguished by alkali, the portions which have beencolored with the first color are decolored at the same time as thedevelopment of the resist by alkali. In other words, since the treatmentby separate two steps can be conducted in one step, the number of thesteps can be reduced and thus the process becomes convenient. Suchalkaline developer includes sodium hydroxide, potassium hydroxide andother alkaline developers on the market. In this embodiment, it isnecessary that the dye of the first color can be decomposed orextinguished by alkali, but it is not necessary that the dyes of othercolors and the black mask are decomposed or extinguished by alkali.

An overcoat layer may be formed on the inorganic active layer 2 whichhas been colored, if necessary. The overcoat layer can be prepared fromhard and transparent resins, such as acrylic resins, melamine resins,epoxy resins, silicon resins, unsaturated polyester resins, isocyanateresins, polyimide, polysiloxanes and ultraviolet curable resins. Also,inorganic materials, such as lithium silicate and sodium silicate, maybe coated.

Instead of forming the overcoat layer, the transparent substrate whichhas been dyed may be immersed in an aqueous solution of nickel acetateand the like and then dried and heated to lose the activity of theinorganic active layer, whereby fixing the dye to the inorganic activelayer 2.

The above described order of the dyeing of the respective colors of R, Gand B is merely illustrative and the order of the dyeing of therespective colors of R, G and B is not especially limited.

PREFERRED EXAMPLES Example 1

An alumina layer 5 to 10 μm thick was formed on a transparent glasssubstrate 1.1 mm thick by the sol-gel method.

Then, the substrate was immersed in a bath of a blue dye C.I. Acid Blue112 at about 60° C. for about 10 minutes to dye all over the surface ofthe alumina layer in blue and washed followed by drying.

Next, a photoresist was formed on the portions other than the portionswhich were to be dyed in green, and the substrate was immersed in30%-nitric acid for 30 seconds at room temperature to decolor the bluedye on the portions which were not covered with the photoresist.

Subsequently, the substrate was immersed in a bath of a green dye C. I.Acid Green 41 at about 40° C. for about 10 minutes to dye the portionswhich had been decolored in green and then washed and dried followed byremoving the photoresist with acetone.

A photoresist was then formed on the portions other than the portionswhich were to be dyed in red, and the substrate was immersed in30%-nitric acid for 30 seconds at room temperature to decolor the bluedye on the portions which were not covered with the photoresist, of thealumina layer.

The substrate was immersed in a bath of a red dye C.I. Acid Red 13 atabout 40° C. for about 10 minutes to dye the portions, which had beendecolored, of the alumina layer in red and then washed and dried.

Next, after the photoresist had been removed with acetone, athermosetting melamine resin was coated in a thickness of 0.5 to 1.0 μmto form an overcoat layer, whereby finishing the color filter.

Example 2

The alumina layer was formed on a transparent glass substrate and dyedin the respective colors of B, G and R in the same manner as in EXAMPLE1.

A photoresist was then formed on the portions other than the portions onwhich the black mask was to be formed, and the substrate was immersed in30%-nitric acid at room temperature to decolor the dye on the portions,which had not been covered with the photoresist, of the alumina layer.

Next, the transparent glass substrate was immersed in a mixture solutioncomprising a solution mixture of the following solutions 1 and 2 in aratio of 1:1 for 2 minutes to form a black mask on the portions, whichhad been decolored, of the alumina layer. Subsequently, the portionshaving a metallic gloss were wiped off with cloth and then washed anddried.

    ______________________________________                                        Solution 1:                                                                   Silver nitrate         20     g                                               Ammonia water     Suitable quantity                                           Water                  1,000  ml                                              Solution 2:                                                                   Sodium potassium tartarate                                                                      100 g/300 ml                                                Water             Until 700 ml in all                                         ______________________________________                                    

Next, after the photoresist was removed with acetone, a thermosettingmelamine resin was coated in a thickness of 0.5 to 1.0 μm to form anovercoat layer, whereby finishing the color filter.

Example 3

An alumina layer was formed on a transparent glass substrate and dyed inthe respective colors of B, G and R to decolor the dye on the portionson which the black mask was to be formed, as described in Example 2.

Next, the substrate was immersed in a bath of a black dye C.I. AcidBlack 107 at 40° C. for about 30 minutes to dye the portions, which hadbeen decolored, of the alumina layer in black and washed followed bydrying.

After the photoresist was removed with acetone, a thermosetting melamineresin was coated in a thickness of 0.5 to 1.0 μm to form the overcoatlayer, whereby finishing the color filter.

Example 4

An alumina layer 5 to 10 μm thick was formed on the transparent glasssubstrate 1.1 mm thick by the sol-gel method.

The substrate was then immersed in a bath of a blue dye C.I. Acid Blue112 at about 60° C. for about 10 minutes to dye all over the surface ofthe alumina layer in blue and washed followed by drying.

Next, the photoresist was formed on the portions other than the portionson which the black mask was to be formed, and the substrate was immersedin 30%-nitric acid for 30 seconds to room temperature to decolor theblue dye on the portions, which had not been covered with thephotoresist, of the alumina layer.

Subsequently, the substrate was immersed in a bath of a black dye (C.I.Mordant Black 9) at about 70° C. for about 30 minutes to dye theportions, which had been decolored, of the alumina layer in black andthen washed and dried followed by removing the photoresist with acetoneto form the black mask.

A photoresist was formed on the portions other than the portions whichwere to be dyed in green, and the substrate was immersed in 30%-nitricacid for 30 seconds at room temperature to decolor the blue dye on theportions, which had not been covered with the photoresist, of thealumina layer.

The substrate was then immersed in a bath of a green dye C.I. Acid Green41 at about 40° C. for about 10 minutes to dye the portions, which hadbeen decolor, of the alumina layer in green and then washed and driedfollowed by removing the photoresist with acetone.

Next, a photoresist was formed on the portions other than the portionswhich were to be dyed in red and the substrate was immersed in30%-nitric acid for 30 seconds at room temperature to decolor the bluedye on the portions, which had not been covered with the photoresist, ofthe alumina layer.

Successively, the substrate was immersed in a bath of a red dye C.I.Acid Red 13 at about 40° C. for about 10 minutes to dye the portions,which had been decolored, of the alumina layer in red and then washedfollowed by drying.

Next, after the photoresist had been removed with acetone, athermosetting melamine resin was coated in a thickness of 0.5 to 1.0 μmto form the overcoat layer, whereby finishing the color filter.

Example 5

An alumina layer was formed on the transparent glass substrate in thesame manner as in Example 4 to obtain the substrate which was dyed inblue all over the surface thereof.

A photoresist was then formed on the portions other than the portions onwhich the black mask was to be formed and simultaneously the dye on theportions, which were not covered with the photoresist, of the aluminalayer was decolored.

Next, the substrate was immersed in a solution of palladium-tin catalystfor 1 minute and then the resist was removed. Subsequently, thesubstrate was immersed in a 3%-aqueous solution of NaOH to activate thecatalyst.

Next, the substrate was immersed in a nickel-plating bath at 80° C. for1 minute to obtain the black mask formed by the Ni-plating.

Next, the dyeing processes in R and G were conducted in the same manneras in Example 4 and a thermosetting melamine resin was coated in athickness of 0.5 to 1.0 μm to form the overcoat layer, whereby finishingthe color filter.

Example 6

An alumina layer 5 to 10 μm thick was formed on the transparent glasssubstrate 1.1 mm thick by the sol-gel method.

The substrate was then immersed in a bath of a red dye C.I. Acid Red 9at about 60° C. for about 10 minutes to dye the alumina layer in red allover the surface thereof and then washed followed by drying.

Next, A photoresist was spin-coated and the pattern of the black maskwas exposed and developed to form the photoresist on the portions otherthan the portions on which the black mask was to be formed andsimultaneously the red dye on the portions, which had not been coveredwith the photoresist, of the alumina layer was decolored.

Subsequently, the black mask was formed by the chemical plating in thesame manner as in Example 2 and the photoresist was removed.

A photoresist was then spin-coated and the pattern of the second color,that is a green color, was exposed and developed to form the photoresiston the portions other than the portions which were to be dyed in greenand simultaneously the red dye of the portions, which had not beencovered with the photoresist, of the alumina layer was decolored.

Successively, the substrate was immersed in a bath of a green dye C.I.Acid Green 41 at about 40° C. for about 10 minutes to dye the portions,which had been decolored, of the alumina layer in green and then washedand dried followed by removing the photoresist with acetone.

An photoresist was spin-coated and the pattern of the third color, thatis a blue color, was exposed and developed to form the photoresist onthe portions other than the portions which were to be dyed in blue andsimultaneously the red dye on the portions, which had not been coveredwith the photoresist, of the alumina layer was decolored.

The substrate was then immersed in a bath of blue dye C.I. Acid Blue 112at about 60° C. for about 10 minutes to dye the portions, which had beendecolored, of the alumina layer in blue and then washed followed bydrying.

Next, after the photoresist was removed with acetone, a thermosettingmelamine resin was coated in a thickness of 0.5 to 1.0 μm to form theovercoat layer, whereby finishing the color filter with the black maskformed by the chemical plating.

Example 7

A photoresist was formed on the portions other than the portions, onwhich the black mask was to be formed, in the same manner as in Example6 and simultaneously the dye of the portions other than the portions, onwhich the photoresist had been formed, was decolored.

The black mask was then formed by Ni-plating in the same manner as inExample 5.

Next, the treatment was conducted in the same manner as in Example 6 toobtain the color filter.

Example 8

The treatment was conducted in the same manner as in Example 7 exceptingthat the black mask was formed with black dye in place of Ni-plating toobtain the color filter.

INDUSTRIAL APPLICABILITY

According to the present invention, the color filter used in a liquidcrystal television and other color displays can be efficiently produced.

We claim:
 1. A method of producing a color filter, which comprises thefollowing steps conducted in turn:(a) a step of forming an inorganicactive layer on a transparent substrate; (b) a step of dyeing saidinorganic active layer in a first color; (c) a step of forming a resiston portions of said inorganic active layer other than portions which areto be dyed in a second color; (d) a step of conducting a decoloringtreatment to decolor exposed portions of said inorganic active layer;(e) a step of dyeing said exposed portions of said inorganic activelayer in the second color; (f) a step of removing said resist; (g) astep of forming a resist on portions of said inorganic active layerother than portions which are to be dyed in a third color; (h) a step ofconducting a decoloring treatment to decolor exposed portions of saidinorganic active layer; (i) a step of dyeing said exposed portions ofsaid inorganic active layer in the third color; and (j) a step ofremoving said resist.
 2. A method of producing a color filter, whichcomprises the following steps conducted in turn:(a) a step of forming aninorganic active layer on a transparent substrate; (b) a step of dyeingsaid inorganic active layer in a first color; (c) a step of forming aresist on portions of said inorganic active layer other than portionswhich are to be dyed in a second color; (d) a step of conducting adecoloring treatment to decolor exposed portions of said inorganicactive layer; (e) a step of dyeing said exposed portions of saidinorganic active layer in the second color; (f) a step of removing saidresist; (g) a step of forming a resist on portions of said inorganicactive layer other than portions which are to be dyed in a third color;(h) a step of conducting a decoloring treatment to decolor exposedportions of said inorganic active layer; (i) a step of dyeing saidexposed portions of said inorganic active layer in the third color; (j)a step of removing said resist; (k) a step of forming a resist onportions of said inorganic active layer other than portions on which ablack mask is to be formed; (l) a step of forming the black mask on gapsamong the portions, which have been dyed in the first to third colors,by chemical plating; and (m) a step of removing said resist.
 3. A methodof producing a color filter, which comprises the following stepsconducted in turn:(a) a step of forming an inorganic active layer on atransparent substrate; (b) a step of dyeing said inorganic active layerin a first color; (c) a step of forming a resist on portions of saidinorganic active layer other than portions which are to be dyed in asecond color; (d) a step of conducting a decoloring treatment to decolorexposed portions of said inorganic active layer; (e) a step of dyeingsaid exposed portions of said inorganic active layer in the secondcolor; (f) a step of removing said resist; (g) a step of forming aresist on portions of said inorganic active layer other than portionswhich are to be dyed in a third color; (h) a step of conducting adecoloring treatment to decolor exposed portions of said inorganicactive layer; (i) a step of dyeing said exposed portions of saidinorganic active layer in the third color; (j) a step of removing saidresist; (k) a step of forming a resist on portions of said inorganicactive layer other than portions on which a black mask is to be formed;(l) a step of dyeing between the portions, which have been dyed in thefirst to third colors, in black to form the black mask; and (m) a stepof removing said resist.
 4. A method of producing a color filter, whichcomprises the following steps conducted in turn:(a) a step of forming aninorganic active layer on a transparent substrate; (b) a step of dyeingsaid inorganic active layer in a first color; (c) a step of forming aresist on portions of said inorganic active layer other than portions onwhich a black mask is to be formed; (d) a step of conducting adecoloring treatment to decolor exposed portions of said inorganicactive layer; (e) a step of forming the black mask by chemical platingor dyeing in black; (f) a step of removing said resist; (g) a step offorming a resist on portions of said inorganic active layer other thanportions which are to be dyed in a second color; (h) a step ofconducting a decoloring treatment to decolor exposed portions of saidinorganic active layer; (i) a step of dyeing said exposed portions ofsaid inorganic active layer in the third color; (j) a step of removingsaid resist; (k) a step of forming a resist on portions of saidinorganic active layer other than portions which are to be dyed in athird color; (l) a step of conducting a decoloring treatment to decolorexposed portions of said inorganic active layer; (m) a step of dyeingsaid exposed portions of said inorganic active layer in the third color;and (n) a step of removing said resist.
 5. A method of producing a colorfilter, which comprises the following steps conducted in turn:(a) a stepforming an inorganic active layer on a transparent substrate; (b) a stepof dyeing said inorganic active layer in a first color; (c) a step offorming a resist on portions of said inorganic active layer other thanportions on which a black mask is to be formed; (d) a step of conductinga decoloring treatment to decolor exposed portions of said inorganicactive layer; (e) a step of absorbing a catalyst solution into theinorganic active layer; (f) a step of removing said resist; (g) a stepof activating said catalyst solution; (h) a step of forming a black maskby plating metal; (i) a step of forming a resist on portions of saidinorganic active layer other than portions which are to be dyed in asecond color; (j) a step of conducting a decoloring treatment to decolorexposed portions of said inorganic active layer; (k) a step of dyeingsaid exposed portions of said inorganic active layer in the secondcolor; (l) a step of removing said resist; (m) a step of forming aresist on portions of said inorganic active layer other than portionswhich are to be dyed in a third color; (n) a step of conducting adecoloring treatment to decolor exposed portions of said inorganicactive layer; (o) a step of dyeing said exposed portions of saidinorganic active layer in a third color; and (p) a step of removing saidresist.
 6. A method of producing a color filter, which comprises thefollowing steps conducted in turn:(a) a step of forming an inorganicactive layer on a transparent substrate; (b) a step of dyeing saidinorganic active layer in a first color; (c) a step of forming aphotoresist on portions of said inorganic active layer other thanportions on which a black mask is to be formed and simultaneouslydecoloring portions of said inorganic active layer other than theportions on which said photoresist has been formed; (d) a step offorming the black mask by chemical plating; (e) a step of removing thephotoresist; (f) a step of forming a photoresist on portions of saidinorganic active layer other than portions which are to be dyed in asecond color and simultaneously decoloring portions of said inorganicactive layer other than the portions on which said photoresist has beenformed; (g) a step of dyeing the decolored portions of said inorganicactive layer in the second color; (h) a step of removing thephotoresist; (i) a step of forming a photoresist on portions of saidinorganic active layer other than portions which are to be dyed in athird color and simultaneously decoloring portions other than theportions on which said photoresist has been formed; (j) a step of dyeingthe decolored portions of said inorganic active layer in the thirdcolor; and (k) a step of removing the photoresist.
 7. A method ofproducing a color filter, which comprises the following steps conductedin turn:(a) a step of forming an inorganic active layer on a transparentsubstrate; (b) a step of dyeing said inorganic active layer in a firstcolor; (c) a step of forming a photoresist on portions of said inorganicactive layer other than portions on which a black mask is to be formedand simultaneously decoloring portions of said inorganic active layerother than the portions on which said photoresist has been formed; (d) astep of absorbing a catalyst solution into the inorganic active layer;(e) a step of removing the photoresist; (f) a step of activating saidcatalyst solution; (g) a step of forming said black mask by platingmetal; (h) a step of forming a photoresist on portions of said inorganicactive layer other than portions which are to be dyed in a second colorand simultaneously decoloring portions of said inorganic active layerother than the portions on which said photoresist has been formed; (i) astep of dyeing the decolored portions of said inorganic active layer inthe second color; (j) a step of removing the photoresist; (k) a step offorming a photoresist on portions of said inorganic active layer otherthan portions which are to be dyed in a third color and simultaneouslydecoloring portions of said inorganic active layer other than theportions on which said photoresist has been formed; (l) a step of dyeingthe decolored portions of said inorganic active layer in the thirdcolor; and (m) a step of removing the photoresist.
 8. A method ofproducing a color filter, which comprises the following steps conductedin turn:(a) a step of forming an inorganic active layer on a transparentsubstrate; (b) a step of dyeing said inorganic active layer in a firstcolor; (c) a step of forming a photoresist on portions of said inorganicactive layer other than portions on which a black mask is to be formedand simultaneously decoloring portions other than the portions on whichsaid photoresist has been formed; (d) a step of forming said black maskby dyeing the inorganic active layer in black; (e) a step of removingthe photoresist; (f) a step of forming a photoresist on portions of saidinorganic active layer other than portions which are to be dyed in asecond color and simultaneously decoloring portions of said inorganicactive layer other than the portions on which said photoresist has beenformed; (g) a step of dyeing the decolored portions of said inorganicactive layer in the second color; (h) a step of removing thephotoresist; (i) a step of forming a photoresist on portions of saidinorganic active layer other than portions which are to be dyed in athird color and simultaneously decoloring portions of said inorganicactive layer other than the portions on which said photoresist has beenformed; (j) a step of dyeing the decolored portions of said inorganicactive layer in the third color; and (k) a step of removing thephotoresist.
 9. The method according to any one of claims 1 to 8,wherein said inorganic active layer is obtained by applying a sol, whichis obtained by electrolyzing an aqueous solution of a compound expressedby the following general formula (I) and degelatinizing the electrolyzedsolution, to said transparent substrate and baking the applied sol,

    M(OR.sub.1).sub.m (OR.sub.2).sub.n X.sub.p Y.sub.q         (I)

wherein M is at least one element selected form the group consisting ofmagnesium, calcium, zirconium, titanium, hafnium, germanium, yttrium,aluminum, gallium, tin and silicon; R₁ and R₂, which are the same ordifferent, show a hydrogen atom, an alkyl group or an acyl group,respectively; X and Y, which are the same or different, show a hydrogenatom, a chlorine atom or a hydroxyl group, respectively; m, n, p and qare an integer of 0 to 8, respectively, so as to meet m+n+p+q=a valenceof M.